Selective catalytic activation of non-conductive substrates

ABSTRACT

A process of providing a pattern of a metal on a non-conductive substrate to create loop antennae for wireless articles, for creating circuitry for smart cards, such as phone cards, and for providing electromagnetic shielding of electronic devices is provided. The method comprises the steps of catalyzing the non-conductive substrate by applying a catalytic ink, reducing a source of catalytic metal ions in the catalytic ink to its associated metal, depositing electroless metal on the pattern of catalytic ink on the surface of the substrate; and plating electrolytic metal on the electroless metal layer to produce the desired pattern of metal on the non-conductive substrate. The catalytic ink typically comprises one or more solvents, a source of catalytic metal ions, a crosslinking agent, one or more copolymers, a polyurethane polymer, and, optionally, one or more fillers.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of co-pending applicationSer. No. 10/837,109 filed on Apr. 30, 2004, the subject matter of whichis herein incorporated by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to improved methods for patterningnon-conductive substrates with electrolytic metals. The patternedsubstrates of the invention are used to create loop antennae forwireless articles, to create circuitry for phone cards, and to provideelectromagnetic interference (EMI) shielding for electronic devices.

BACKGROUND OF THE INVENTION

Many electronic applications require patterned metallization ofnonconductive substrates for interconnection among electronic devices.Examples of such applications include high-density packaging (multi-chipmodules), antennas, flex circuits, printed wiring boards, and flat paneldisplays.

Radio Frequency Identification (RFID) is a type of automaticidentification system. The purpose of an RFID system is to enable datato be transmitted by a portable device, called a tag, which is read byan RFID reader and processed according to the needs of a particularapplication. A basic RFID system consist of three components:

-   -   An antenna or coil    -   A transceiver (with decoder)    -   A transponder (RF tag) electronically programmed with unique        information

Wireless articles, including tags, identification badges, smart cards,etc., are in wireless communication with a base unit or reader via aradio-frequency (RF) communication link. These articles can be used forelectronic identification and tracking of articles, persons andtransactions. RF transmissions transmitted by the base unit may bereceived by an antenna on the wireless article, or RF transmissionstransmitted by the wireless article by an antenna thereon may bereceived by the base unit, or RF transmissions by each of the wirelessarticle and the base unit may be received by the other one thereof.

RFID tags are categorized as either active or passive. Active RFID tagsare powered by an internal battery and are typically read/write, i.e.,tag data can be rewritten and/or modified. An active tag's memory sizevaries according to application requirements. Passive RFID tags operatewithout a separate external power source and obtain operating powergenerated from the reader.

The significant advantage of all types of RFID systems is thenoncontact, non-line-of-sight nature of the technology. Tags can be readthrough a variety of substances such as snow, fog, ice, paint, crustedgrime, and other visually and environmentally challenging conditions,where barcodes or other optically read technologies would be useless.

In each case, the RF signals either received or transmitted by thewireless article are received or transmitted by an antenna thereon.Because wireless articles are usually desired to be small in size, theantenna thereon is also small in size. The conductive coil pattern ofthe RF antenna allows the antenna to receive and radiate energies in theradio frequency range. The sensitivity of the antenna to small amplitudeRF signals and the amplitude of the RF signals transmitted by theantenna are a direct function of the area enclosed by the antenna loopand the number of turns of the conductor forming the loop. For a smalltag or badge, the size limits the area that an antenna loop can enclose,thereby limiting the RF performance of the antenna. Typically, theantenna is optimized to transmit and receive energy in a relativelynarrow portion of the radio frequency range. Often, the radio frequencyantenna is connected to an integrated circuit. The integrated circuitreceives energy from a detector unit, modulates the energy with anidentification pattern stored in the integrated circuit, and thenretransmits the modulated energy to the detector unit. RF identificationtags typically operate in the frequency range of 100 KHz to 3 GHz, orhigher.

Various methods of assembling wireless articles and of forming RFantennae and circuitry on such articles are described in the prior art.

U.S. Pat. No. 6,333,721 to Altwassen, the subject matter of which isherein incorporated by reference in its entirety, describes a method offorming an RF antenna by stamping a conductive coil out of a sheet ofmetal. The drawback of this method is that the production of the metalcoil may result in a large amount of scrap metal. In addition, the RFantennae produced by stamping from a sheet of metal may be less flexiblethan desired for many applications.

Another way that has been suggested for forming RF antennae is to usestrip-back techniques that are commonly used in printed circuit boardfabrication. In printed circuit board fabrication, a layer of conductivematerial, i.e., metal, is formed on top of the substrate and the areasnot used for the antenna are stripped away. This method tends to bewasteful when used to produce radio frequency antennae, because theradio frequency coil antenna tends to cover only about 10% of thesurface area of the substrate. In contrast, typical printed circuitboard implementations require coverage areas of about 70-80%.

Still another way of forming RF antennae on non-conductive substrates isdescribed in U.S. Pat. No. 6,662,430 to Brady et al., the subject matterof which is herein incorporated by reference in its entirety, whereinelectrical circuitry is connected to an antenna, which is made of acomposite material, and the composite material is connected toelectrical circuitry at points. The antenna is made by screening a pasteof metal powder, polymer material, and solvent through a screen onto asubstrate. While the paste is still wet, the electrical circuitry isbonded to the material by contacting electrical contacts of theelectrical circuitry with the wet paste, and then driving off thesolvent and/or curing the polymer matrix material.

WO 01/69717 to RCD Technology, Inc., the subject matter of which isherein incorporated by reference in its entirety, describes a process offorming RF antennae using conductive inks. The conductive ink is printedin a RF antenna coil pattern on top of the substrate, and is then cured.The printed antennae may then be used as is or electrodes may beattached to the conductive ink pattern and a metal layer thenelectroplated on top of the conductive ink pattern.

A fundamental problem with RF tags and identification devices is thatthe cost of the tag/card must be reduced to a level small compared tothe cost of the product to which the tag is attached, which will thenallow many more tags to be used and so that high volume production cancut the costs even further. The cost of the tags is the cost of thesemiconductor chip, the antenna, the substrate supporting the antennaand chip, and the attachment cost. As the use such devices becomes moreand more widespread, there remains a need in the art for greaterefficiency in the process while reducing the cost of production.

The inventors of the present invention have discovered that antennae andcircuitry may advantageously be produced by using a novel catalytic inkformulation for forming the antennae and circuitry, which may then beplated with an electroless plating composition followed by anelectrolytic plating composition. The inventors have also surprisinglydiscovered that the novel catalytic ink formulations of the inventioncan be beneficially used to provide electromagnetic interference (EMI)shielding on electronic devices, followed by plating with an electrolessmetal plating composition.

Method of providing EMI shielding on electrical devices are well knownin the prior art. U.S. Pat. No. 6,697,248 to Luch, the subject matter ofwhich is herein incorporated by reference in its entirety lists severalof the more common methods used for EMI shielding as well as theproblems associated with some of these methods.

The typical methods to shield electronic devices consist of surroundingthe electronic components with a conductive barrier which reflectsand/or absorbs the radiation. The simplest in concept is to select ametal housing or cabinet for the shield. Sheet metal liners can becombined with the appeal of a plastic exterior, but tend to be expensiveand have to be attached to the plastic housing which complicates andlengthens the assembly process.

A number of methods have been developed to provide shielding to plasticcomponents, including the use of conductive paints, which can be appliedwith conventional spray painting equipment, and vacuum metallization,which involves heating and vaporizing the conductive metal so that themetal then condensed on the surface of the plastic.

An alternative method for imparting EMI shielding to plastics involvesthe use of electroless plating to chemically coat a nonconductivesurface such as a plastic with a continuous metallic film. A series ofchemical steps involving etchants and catalysts is used to prepare thenon-conductive plastic substrate to accept a metal layer deposited bychemical reduction of metal from solution. The process usually involvesdepositing a thin layer of highly conductive copper followed by a nickeltopcoat which protects the copper sublayer from oxidation and corrosion.Because electroless plating is an immersion process, uniform coatingscan be applied to almost any configuration regardless of size orcomplexity without a high reliance on operator skill. Electrolessplating also provides a highly conductive pure metal surface whichresults in relatively good shielding effectiveness. In addition,electrolessly plated parts can be subsequently electroplated, althoughelectroplating is generally not used unless a part also has certaindecorative or functional requirements.

However, the process comprises many steps and is very sensitive toprocessing variables used to fabricate the plastic substrate. Inaddition, selective metallization can be difficult, especially oncomplex parts, since the electroless plating may tend to coat anyexposed surface unless the overall process is carefully controlled.While many attempts have been made to simplify the process of plating onplastic substrates, there remains a need in the art for improved methodsof plating plastic substrates to provide EMI shielding.

While catalytic ink formulations and plating catalysts have been widelydisclosed in the prior art, there remains a need in the art for improvedcatalytic ink formulations that can be used for forming RF antennae,phone card circuitry, and to provide EMI shielding of electronicdevices.

U.S. Pat. No. 3,414,427 to Levy, the subject matter of which is hereinincorporated by reference in its entirety, describes a method ofcatalyzing a surface of a material to be plated by a chemical reductionplating process. The method uses a catalyst comprising a complex ofpalladium chloride dissolved in an organic solvent (i.e., acetone).However the catalyst is not very effective in catalyzing non-conductive(plastic) substrates.

U.S. Pat. No. 4,368,281 to Brummett et al., the subject matter of whichis herein incorporated by reference in its entirety, describe a processfor making flexible printed circuits on flexible substrates. Brummett etal. describe an ink formulation comprising an appropriate coordinationcomplex of palladium. This complex is depicted by a formulaL_(m)PdX_(n), wherein L is a ligand or unsaturated organic group, Pd isa palladium metal base of the complex, X is a halide, alkyl group, orbidentate ligand and m and n are integers wherein m is from 1 to 4 and nis from 0 to 3. However, there is no suggestion that the catalytic inkformulation described by Brummett et al. can be used for forming RFantennae and circuitry for wireless articles.

U.S. Pat. No. 5,288,313 to Portner, the subject matter of which isherein incorporated by reference in its entirety, describes a platingcatalyst that comprises a mixture of catalytic particles dispersed in aliquid coating composition, and is useful for the formation ofselectively deposited metal coatings. The catalytic particles are formedfrom a reduced metal salt that is an electroless plating catalyst coatedon an inert particulate carrier. The process of the invention permitsplating at a good plating rate and results in a deposit that is andremains strongly adhered to its underlying substrate during prolongeduse. However, the catalyst must be applied as a paste and the processfurther requires a step of solvating (i.e., softening) thenon-conductive substrate prior to application of the catalyst.

U.S. Pat. No. 5,378,268 to Wolf et al., the subject matter of which isherein incorporated by reference in its entirety, describes a primercomposition for chemical metallization of substrate surfaces without thenecessity of prior etching with an oxidant. The primer compositioncomprises a) a film former based on a polyurethane system; b) anadditive having a specific surface tension; c) an ionic and/or colloidalnoble metal or organometallic covalent compound thereof; d) a filler;and e) a solvent. However, there is no suggestion that the primerdescribed by Wolf et al. can be selectively applied to produce RFantennae or smart card circuitry.

U.S. Pat. No. 6,461,678 to Chen et al., the subject matter of which isherein incorporated by reference in its entirety also describes aprocess for applying a catalyst solution comprising a solvent, acarrier, and metal catalyst ions to the surface of a substrate. Thecatalyst solution can cover the entire surface of the substrate or canbe selectively applied to only a portion of a surface of substrate. Theconcentration of solvent in the layer of catalyst solution on thesurface of substrate can be reduced by heating the substrate. Metallicclusters can be formed in the remaining catalyst layer by furtherheating the substrate. Electroless plating can then deposit metal ontothe portion of the surface of substrate coated with the catalystsolution. Electrolytic plating can then deposit additional metal ontothe portion of the surface of substrate coated with the catalystsolution. However, Chen et al. also do not suggest that the catalystdescribed in their invention can be used in a process to produce RFantennae or smart card circuitry.

Thus, there remains a need in the art for an improved catalytic inkcomposition and for an improved process of using the catalytic inkcomposition to produce RF antennae and circuitry for wireless articlesand to provide improved EMI shielding of electronic devices thatovercomes many of the drawbacks of the prior art.

SUMMARY OF THE INVENTION

The present invention generally comprises a method for providing apattern of a metal on a non-conductive substrate comprising the stepsof:

-   -   a) catalyzing the non-conductive substrate by applying a        catalytic ink comprising a source of catalytic metal ions in the        desired pattern on a surface of the non-conductive substrate;    -   b) reducing the source of catalytic metal ions in the catalytic        ink to its associated metal;    -   c) depositing electroless metal on the pattern of catalytic ink        on the surface of the substrate; and    -   d) plating electrolytic metal on the electroless metal layer to        a desired thickness to produce the desired pattern of metal on        the non-conductive substrate.

In a preferred embodiment, the catalytic metal ions comprise ionicpalladium, which may be reduced to palladium. Other catalytic metalions, including gold, platinum, silver and copper that may be reduced totheir associated metal are also usable in the invention. Alternatively,catalytic metal itself may be directly included in the catalytic ink.

In one embodiment, the catalytic ink is screen printed in the desiredpattern, i.e., the antenna pattern, and allowed to dry. Other printingmeans, including gravure, lithography and flexography may also be usedto print the catalytic ink in the desired pattern. In anotherembodiment, the catalytic ink is printed in a desired pattern to provideEMI shielding.

The catalytic ink of the invention typically comprises:

-   -   a) one or more solvents;    -   b) a source of catalytic metal ions such as palladium, gold,        platinum, silver, copper, etc.;    -   c) a crosslinking agent;    -   d) one or more copolymers;    -   e) a polyurethane polymer; and    -   f) optionally, one or more fillers.

Alternatively, the pattern of metal on the non-conductive substrate maybe providing using a method comprising the steps of:

-   -   a) catalyzing the non-conductive substrate by applying a        catalytic ink comprising a source of catalytic metal ions in a        solid pattern with an outline of the desired pattern on a        surface of the non-conductive substrate;    -   b) reducing the source of catalytic metal ions in the catalytic        ink to its associated metal;    -   c) depositing electroless metal on the pattern of catalytic ink        on the surface of the substrate;    -   d) plating electrolytic metal on the electroless metal layer to        a desired thickness to produce the desired pattern of metal on        the non-conductive substrate    -   e) printing a UV etch resist with the desired pattern; and    -   f) etching away the plated metal between the resist to define        the desired circuit.

In a preferred embodiment, the catalytic metal ions comprise ionicpalladium, which may be reduced to palladium metal. Other catalyticmetal ions, including gold, platinum, silver, and copper that may bereduced to their associated metal are also usable in the invention.Alternatively, catalytic metal itself may be directly included in thecatalytic ink.

The catalytic ink formulation of the invention may also be used to platecircuitry on phone cards without the use of conventional palladiumactivation tanks.

In this embodiment, the phone card is manufactured according to thefollowing steps:

-   -   a) applying catalytic ink comprising a source of catalytic metal        ions to the non-conductive substrate and allowing the catalytic        ink to dry;    -   b) reducing the source of metal (i.e., palladium) in the ink to        metal in a zero valence state (i.e., palladium metal) as        described above;    -   c) printing a resist on the phone card to produce circuitry with        gaps in the lines for “fuses;”    -   d) depositing electroless nickel on the exposed (non-covered        areas of the catalytic ink); and    -   e) plating electrolytic tin/lead on top of the electroless        nickel.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts an RF antennae on a non-conductive substrate manufacturedby the process of the instant invention.

FIG. 2 depicts a different view of the RF antennae on the non-conductivesubstrate manufactured by the process of the instant invention.

FIG. 3 depicts a phone card made by the process of the instantinvention.

FIG. 4 depicts the location of measurements of the thickness of thecopper deposit at six locations on the RF antennae.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

The present invention relates to various methods of providing a patternof a metal on a non-conductive substrate. The present invention can beused for creating loop antennae for wireless articles, for creatingcircuitry for smart cards, such as phone cards, and for providing EMIshielding on electronic devices.

In a first embodiment, the method comprises the steps of:

-   -   a) catalyzing the non-conductive substrate by applying a        catalytic ink comprising a source of catalytic metal ions in the        desired pattern on a surface of the non-conductive substrate;    -   b) reducing the source of catalytic metal ions in the catalytic        ink to its associated metal;    -   c) depositing electroless metal on the pattern of catalytic ink        on the surface of the substrate; and    -   d) plating electrolytic metal on the electroless metal layer to        a desired thickness to produce the desired pattern of metal on        the non-conductive substrate.

Preferably the catalytic ink comprises ionic palladium, which may bereduced to palladium metal. Other catalytic metal ions including gold,platinum, silver, and copper that may be reduced to their associatedmetal are also usable in the invention. Alternatively catalytic metalitself may be directly included in the catalytic ink.

In a preferred embodiment, the catalytic ink is screen printed in thedesired pattern, i.e., the antenna pattern, and allowed to dry. Otherprinting means, including gravure, lithography and flexography may alsobe used to print the catalytic ink in the desired pattern. In anotherpreferred embodiment, the catalytic ink is printed in a desired patternto provide EMI shielding on an electronic device substrate.

A typical formulation for the catalytic ink is as follows:

-   -   a) one or more solvents;    -   b) a source of catalytic metal ions, such as palladium, gold,        platinum, silver, copper, etc.;    -   c) a crosslinking agent;    -   d) one or more copolymers;    -   e) a polyurethane polymer; and    -   f) optionally, one or more fillers.

The various ingredients of the ink formulation are discussed in moredetail below.

After the catalytic ink is printed in the desired pattern, the source ofcatalytic metal ions (i.e., palladium), in the ink is reduced to metal(i.e., palladium at a zero valence state), by contacting the catalyzedsubstrate with a suitable reducing agent. Although various reducingagents are usable in the practice of the invention, the reducing agentpreferably comprises sodium borohydride, dimethylamino borane, orhydrazine.

Next, electroless metal is deposited on the pattern of catalytic ink onthe substrate. The electroless metal is generally selected fromelectroless nickel and electroless copper, although other electrolessmetal formulations are also usable in the practice of the invention.Suitable formulations of the electroless plating bath would be wellknown to those skilled in the art.

Finally, electrolytic metal is plated over the electroless metaldeposit. A suitable electrolytic plating bath that is usable in theinvention is an acid copper plating bath. The copper (or other metal) istypically plated to an antenna thickness of between about 0.5 and 0.7mils and is selected to have a resistance of less than about 3.0 ohms.In the alternative, the electroless plating process can be used to buildthe entire desired thickness required.

Because of the difficulties in getting an uniform copper thickness whenplating the antenna coils electrolytically, the invention also includesa second embodiment that may avoid this problem.

In this second embodiment, the method comprises the steps of:

-   -   a) catalyzing the non-conductive substrate by applying a        catalytic ink comprising a source of catalytic metal ions in a        solid pattern with an outline of the desired pattern on a        surface of the non-conductive substrate;    -   b) reducing the source of catalytic metal ions in the catalytic        ink to its associated metal;    -   c) depositing electroless metal on the pattern of catalytic ink        on the surface of the substrate;    -   d) plating electrolytic metal on the electroless metal layer to        a desired thickness to produce the desired pattern of metal on        the non-conductive substrate    -   e) printing a UV etch resist with the desired pattern; and    -   f) etching away the plated metal between the resist to define        the desired circuit.

Preferably the catalytic metal ions comprise ionic palladium, which maybe reduced to palladium metal. Other catalytic metal ions includinggold, platinum, silver, and copper that may be reduced to theirassociated metal are also usable in the invention. Alternativelycatalytic metal itself may be directly included in the catalytic ink);

As in the first embodiment, the catalytic ink is screen printed in thedesired pattern, i.e., the antenna pattern, and allowed to dry. Otherprinting means, including gravure, lithography or flexography may alsobe used to print the catalytic ink in the desired pattern. In apreferred embodiment, the catalytic ink is screen printed in a solidband with the outline of the antenna and allowed to dry.

After the catalytic ink is printed in the desired pattern, the source ofcatalytic metal ions (i.e., palladium), in the ink is reduced to metal(i.e., palladium at a zero valence state) and electroless metal isdeposited on the catalytic ink as described above.

Acid copper is electrolytically plated over the electroless metal forthe solid antenna band to a thickness of about 0.5 to about 0.7 mils.Then, a UV etch resist is applied, preferably by screen printing, in theantenna pattern using a suitable UV etch resist, such as UV screenprintable resists, dry film resists, or other UV resists. Finally, theplated copper is etch away between the resist to define the antennacircuit.

The catalytic ink formulation of the invention may also be used to platecircuitry on phone cards without the use of conventional palladiumactivation tanks. In a preferred embodiment, the phone card substratecomprises polyethylene terephthalate (PET),acrylonitrile-butadiene-styrene (ABS) or polyvinylidine chloride (PVC).

In a preferred embodiment, the PET phone card is manufactured accordingto the following steps:

-   -   a) applying catalytic ink comprising a source of catalytic metal        ions to the PET substrate and allowing the catalytic ink to dry;    -   b) reducing the source of metal (i.e., palladium) in the ink to        its associated metal (i.e., palladium metal) as described above;    -   c) printing a resist on the phone card to produce circuitry with        gaps in the lines for “fuses;”    -   d) depositing electroless nickel on the exposed (non-covered        areas of the catalytic ink; and    -   e) plating electrolytic tin/lead on top of the electroless        nickel.

The catalytic ink can be applied by blank screen printing or other meansthat would be known to one of skill in the art.

Each of the steps of the invention will now be described in greaterdetail below.

As discussed above, a typical formulation of the novel catalytic ink ofthe invention comprises:

-   -   a) one or more solvents;    -   b) a source of catalytic metal ions selected from the group        consisting of palladium, gold, platinum, silver, copper and        combinations of the foregoing;    -   c) a crosslinking agent;    -   d) one or more copolymers;    -   e) a polyurethane polymer or binder; and    -   f) optionally, one or more fillers.

The solvent used in the catalytic ink formulations of the invention istypically a fast evaporating solvent. In general, the solvent of thecatalytic ink may be selected from the group consisting of aromatic andaliphatic hydrocarbons, glycerol, ketones, esters, glycol ethers, andesters of glycol ethers. More particularly, the solvent may comprisetoluene, xylene, glycerol, acetone, methyl ethyl ketone, cyclohexanone,isophorone, butyl acetate, dioctyl phthalate, butyl glycolate, ethyleneglycol monomethyl ether, diethylene glycol dimethyl ether, propyleneglycol monomethyl ether, ethylene glycol acetate, propylene glycolmonomethyl ether-acetate, methyl propyl ketone, methyl amyl ketoneand/or diacetone-alcohol. Other suitable solvents that are inert to theingredients that make up the ink formulation and that are fastevaporating, i.e., having a boiling point of less than about 90° C.would be known to one skilled in the art. Mixtures of one more solventsmay also be used. In a preferred embodiment, the solvent iscyclohexanone. The solvent is generally used in an amount of about 50 toabout 80 percent by weight of the catalytic ink composition, preferablyin an amount of about 55 to about 75 percent by weight. The amount ofsolvent used depends upon the expected cooling method.

In an alternate embodiment, instead of catalytic metal ions, catalyticmetal particles themselves may be included in the ink therebyeliminating the need for subsequent reduction. However, the use of metalparticles may make it more difficult to accurately print the ink.

In a preferred embodiment, the catalytic metal ions comprise palladium,and the source of palladium in the catalytic ink composition of theinvention is generally selected from palladium chloride, palladiumacetate, and palladium sulfate. In one embodiment, the source ofpalladium is a solution of about 10% to about 20% palladium chloride inwater with hydrochloric acid. In an alternate embodiment, the source ofpalladium is a solution of about 0.1% to about 2% palladium acetate incyclohexanone. While the source of palladium is described as beingpalladium chloride or palladium acetate, the invention is not limited tothese compounds. Gold, platinum, silver and copper compounds are alsocontemplated by the inventors and would generally be known to oneskilled in the art. Examples of these compounds can be found in U.S.Pat. No. 5,855,959 to Boecker et al., U.S. Pat. No. 5,518,760 to Ferrieret al., and in U.S. Pat. No. 5,443,865 to Tisdale, et al., the subjectmatter of each of which is herein incorporated by reference in itsentirety. The source of palladium or other catalytic metal is generallyused in an amount of about 1 to about 2 percent by weight of thecatalytic ink formulation.

The crosslinking agent of the catalytic ink formulation typicallycomprises polyisocyanate. Other crosslinking agents may also be suitablefor use in the invention, including peroxides, e.g., benzoylperoxide,methyl ethyl ketone peroxide, etc. As an illustration of isocyanatecrosslinking agents, the following isocyanates are typical: the variousisomeric toluene diisocyanates and mixtures thereof; hexamethyldiisocyanate; diphenylmethane diisocyanate; an adduct oftrimethylolpropane and toluene diisocyanate, etc. The crosslinking agentis generally used in an amount of about 1 to about 3 percent by weight.

When crosslinking with isocyanate, crosslinking occurs through theterminal—OH groups of the ink polyester moiety and a small portionthrough the substrate—OH moiety as well as hydroxyl groups on othercomponents. Inasmuch as an isocyanate may be a polyfunctional isocyanatewith 2 to 4 and even more isocyanate groups, the reaction produces awell crosslinked ink sufficiently adhering to a typical substrate, suchas Mylar® (a polyethylene terephthalate film available from DuPont).

The copolymer may be selected from the group consisting of acryliccopolymers, ethylene copolymers with acrylate or vinyl acetate,chlorinated or unchlorinated copolymers of vinyl chloride and othersimilar compounds, used alone or in combination. In a preferredembodiment, the copolymer comprises vinyl chloride and hydroxylpropylacrylate. The copolymer generally comprises about 3 to about 10 percentby weight of the catalytic ink formulation.

The catalytic ink formulation also comprises a polyurethane polymer. Thepolyurethane polymer is typically dissolved in the solvent of thecatalytic ink formulation, i.e., cyclohexanone. The polyurethane/solventmixture is typically present in an amount of about 3 to about 10 percentby weight of the catalytic ink formulation.

The catalytic ink composition of the invention also contains one or morefillers that may be selected from the group consisting of talc, oxidesof manganese, titanium, magnesium, aluminum, bismuth, copper, nickel,tin, zinc, and silicon, silicates, bentonites, chalk, conductive carbonblack, and mixtures of the foregoing. In a preferred embodiment, the oneor more fillers comprise talc and fumed silica. The fillers generallycomprise about 10 to about 30 percent by weight of the catalytic inkformulation. Preferably about 15 to about 25 percent by weight talc andabout 0 to about 5 percent by weight of fumed silica is used in thecatalytic ink formulation of the invention.

The catalytic ink formulation may be applied to the substrate in avariety of ways, such as dipping, spraying, slide coating, slot coating,roll coating, Meyer-rod coating, gravure coating, and draw-downprocesses known to those skilled in the art can coat an entire surfaceof the substrate. Full coating can result in full metallization of thesubstrate surface. Etching processes known to those skilled in the artcan be used to remove selected portions of the full coating if apatterned metallization is required. Alternatively, processes such asscreen printing, flexographic printing, plotting, ink-jet printing, andgravure printing can apply catalyst solution to only selected portionsof the substrate surface. The substrate surface will be metallized onlywhere the catalyst solution was applied. Accordingly, a patternedapplication of catalyst solution can result in patterned substratemetallization.

The viscosity of the (thixotropic) catalytic ink formulation of theinvention is preferably in the range of about 1000 to about 8000 cp,preferably about 3000 to about 6000 cp (at a shear rate of 200 sec⁻¹),to allow the ink to be screen printed onto the substrate. If othermeans, such as gravure, lithography, or flexography, are used forprinting the catalytic ink formulation onto the substrate, the viscosityof the catalytic ink formulation is adjusted accordingly for the chosenprinting method.

The non-conductive substrate may be formed from a polymer, such aspolyimide, polyethylene terephthalate (PET), Mylar®, polyester,polycarbonate, ABS, PVC, paper or coated paper and other similarsubstrates that are known in the art. It is preferable to use an elasticmaterial so that the system is flexible. In one preferred embodiment,the non-conductive substrate is polyethylene terephthalate. Thesubstrate is typically about 0.75 mm thick (about 0.03 inch thick), butmay range between 0.05 and 1.0 mm thick (about 0.002 to 0.040 inchthick, i.e. 2-40 mils). Other substrates which may be employed includepolyimide, polyimide-amide, polyparabanic acid, polycarbonate,polysulfones, polyamine, cellulose triacetate, etc. In the case ofproviding EMI shielding, the electronic device substrate is typicallycomposed of PET or polyimide.

Next, the source of the catalytic metal ions in the catalytic inkformulation is reduced to its associated metal (otherwise known as“activation”) using a suitable reducing/activating agent. The reducingagent preferably comprises sodium borohydride. Other reducing agentsthat may be usable in the practice of the invention include hydrazine,hydrazine hydrate, hydrazine sulfate with sodium hydroxide, anddihydrazine sulfate.

Activation accomplishes several important tasks:

-   -   1) It produces catalytic metallic (i.e., palladium) clusters by        reducing the catalytic metal ion to its associated metal and by        diffusion of the metal to form clusters by nucleation and        growth;    -   2) It polymerizes or otherwise cures the polymer carrier in the        catalyst coating to foster cohesive strength within the cured        carrier; and    -   3) It fosters interdiffusion of molecules between the substrate        and the polymer carrier, causing enhanced adhesion between the        substrate and the cured polymer carrier.

After activation, an electroless plating processes can be used todeposit metal onto the catalyzed and activated substrate. Electrolessplating processes are generally well known to those skilled in the art.The electroless metal that is plated over the catalytic ink is typicallyselected from the group consisting of electroless copper, electrolessnickel, and combinations thereof. Bath compositions for electrolesscopper are disclosed, for example, in U.S. Pat. No. 4,368,281 toBrummett et al., the subject matter of which is herein incorporated byreference in its entirety. Bath compositions for other metals which maybe deposited electroless deposition, including gold, silver, andpalladium, are also disclosed in the prior art, such as in U.S. Pat. No.3,937,857 to Brummett et al., the subject matter of which is hereinincorporated by reference in its entirety.

Electrolytic plating is then used to deposit additional metal to thedesired thickness on the seed metal layer formed by electroless plating.Electrolytic plating is more efficient (has a higher plating rate) thanelectroless plating. Electrolytic plating processes comprise applying anelectric current through an anode to provide electrons needed in thereduction chemical reaction at the cathode and are known to thoseskilled in the art.

The electrolytic metal is generally plated using an acid copper platingbath. Alternatively, the copper deposit may be further plated with anelectroless deposit of palladium or gold. Suitable electrolytic platingbaths are also described in U.S. Pat. No. 4,368,381 to Brummett et al.,the subject matter of which is herein incorporated by reference in itsentirety.

Typically, the resistance of the electrolytically plated metal depositis less than about 3.0 ohms.

FIGS. 1-3 depict various views of the RF antennae and circuitry producedon non-conductive substrates using the process of the instant invention.FIGS. 1 and 2 set forth samples of two RF antennae produced according tothe process of the instant invention. For each of the RF antennae,measurements of thickness of the copper deposit were obtained at sixlocations on the RF antenna (these six locations are set forth in FIG.4). The results of these measurements are presented in Tables 1 and 2.TABLE 1 Readings Taken on RF Antenna depicted in FIG. 1 Reading mil Cu 11.321 2 0.963 3 0.469 4 0.261 5 0.193 6 0.183

TABLE 2 Readings Taken on RF Antenna depicted in FIG. 2 Reading mil Cu 10.522 2 0.503 3 0.812 4 0.911 5 0.832 6 0.659

FIG. 3 depicts the circuitry of an actual phone card. Measurements ofthickness of the electrolytic tin/lead deposit were obtained at fivelocations phone card circuitry, and the results are presented in Table3. TABLE 3 Readings Taken on Phone Card Circuitry Depicted in FIG. 3Reading mil SnPb % Sn % Pb 1 0.413 79.600 20.402 2 0.424 78.763 21.242 30.426 78.374 21.631 4 0.431 78.324 21.682 5 0.434 79.071 20.935 Average0.426 78.826 21.178

In the specific embodiment of providing EMI shielding on anon-conductive substrate, the catalytic ink of the invention is appliedto the non-conductive substrate preferably by screen printing to providethe catalytic ink in selected areas. If desired, other printing methods,such as gravure, lithography, and flexography can be used in place ofscreen printing. The catalytic ink is then allowed to dry and is reducedto catalytic metal as described above. Electroless metal is thendeposited in the pattern of the catalytic ink on the non-conductivesubstrate to a depth of approximately 0.5 to 2.0 microns, preferablyabout 1 micron (40 microinches). Other thicknesses of electroless metalcan also be deposited on the catalytic ink. In addition, multiple layersof catalytic ink can be deposited if desired. It is well within theknowledge of a skilled artisan to choose the metal and the desiredthickness depending on the particular application. In a preferredembodiment, the electroless metal is electroless copper.

If desired, a crosshatch tape adhesion test may be conducted to evaluatethe adhesion of the coating on the non-conductive substrate. The tapeadhesion test may be performed according to ASTM D-3359.

In order to produce a catalytic ink composition that has a long shelflife, the catalytic ink may be used as a two-component system, whereinthe reactants are stored in separate formulations, which are then mixedonly just before application. The reaction then takes placespontaneously or is accelerated by heat and/or a suitable catalyst.

1. A method of plating on a non-conductive substrate, the methodcomprising the steps of: a) applying a catalytic ink to at least aportion of a surface of the non-conductive substrate, wherein thecatalytic ink comprises: i) a solvent; ii) a source of catalytic metalions; iii) a crosslinking agent; iv) a copolymer; and v) a polyurethanepolymer; b) reducing the source of catalytic metal ions to itsassociated metal with a suitable reducing agent; and c) plating metal onthe catalytic ink applied to the portion of the surface of thenon-conductive substrate.
 2. The method according to claim 1, whereinthe catalytic ink is applied by screen printing, gravure, lithography orflexography.
 3. The method according to claim 1, wherein the solvent isselected from the group consisting of aromatic and aliphatichydrocarbons, glycerol, ketones, esters, glycol ethers, and esters ofglycol ethers.
 4. The method according to claim 3, wherein the solventis selected from the group consisting of toluene, xylene, glycerol,methyl ethyl ketone, cyclohexanone, butyl acetate, dioctyl phthalate,butyl glycolate, ethylene glycol monomethyl ether, diethylene glycoldimethyl ether, propylene glycol monomethyl ether, ethylene glycolacetate, propylene glycol monomethyl ether-acetate, acetone, isophorone,methyl propyl ketone, methyl amyl ketone, diacetone-alcohol, andcombinations of the foregoing.
 5. The method according to claim 4,wherein the solvent is cyclohexanone.
 6. The method according to claim1, wherein the catalytic metal ions are selected from the groupconsisting of palladium, gold, silver, platinum, copper, andcombinations of the foregoing.
 7. The method according to claim 6,wherein the catalytic metal ions comprise palladium.
 8. The methodaccording to claim 7, wherein the source of palladium is selected fromthe group consisting of palladium dichloride and palladium acetate. 9.The method according to claim 8, wherein the source of palladium is asolution of about 10% to about 20% palladium dichloride in water withhydrochloric acid.
 10. The method according to claim 8, wherein thesource of palladium is a solution of about 0.1% to about 2% palladiumacetate in cyclohexanone.
 11. The method according to claim 1, whereinthe crosslinking agent is a polyisocyanate.
 12. The method according toclaim 1, wherein the copolymer comprises vinyl chloride andhydroxylpropyl acrylate.
 13. The method according to claim 1, whereinthe catalytic ink comprises one or more fillers selected from the groupconsisting of talc, oxides of manganese, titanium, magnesium, aluminum,bismuth, copper, nickel, tin, zinc, and silicon, silicates, bentonites,chalk, carbon black, and combinations of the foregoing.
 14. The methodaccording to claim 13, wherein the one or more fillers comprise talc andfumed silica.
 15. The method according to claim 1, wherein thenon-conductive substrate is selected from the group consisting ofpolyimides and polyethylene terephthalate.
 16. The method according toclaim 1, wherein the source of catalytic metal ions is reduced to itsassociated metal with a reducing agent selected from the groupconsisting of sodium borohydride, hydrazine, hydrazine hydrate,hydrazine sulfate, and dihydrazine sulfate.
 17. The method according toclaim 16, wherein the reducing agent is sodium borohydride.
 18. Themethod according to claim 1, wherein the metal is selected from thegroup consisting of electroless copper, electroless nickel, andcombinations thereof.
 19. The method according to claim 18, wherein themetal is electroless copper.
 20. The method according to claim 1,wherein the metal is plated to a thickness of about 0.5 to 1.5 microns.21. An electromagnetic interference coated substrate produced by theprocess of claim 1.